Border control: Courtesy of electronics designers

-April 18, 2017

I am not going to get political here, but if there is going to be better border control, why a wall or fences? We’re electronics designers, so let’s strengthen border control with clever electronic design architectures.

Here are some possible cost-effective ideas from which we can expand upon.

Rayleigh backscattering1

Rayleigh scattering is the scattering of light off molecules, waves, particles, or signals in the air or in optical fiber back in the direction from which they emanated. Faults in optical fiber can be detected with this phenomenon via minute changes in the fiber index.

By using a single-mode, buried fiber optic cable in a 100m swath around the cable and for a range of over 40 km over the length of that cable, unique backscatter signatures for people walking, vehicles moving and even digging (such as in tunnels for drug traffickers) are clearly identifiable from each other and can be precisely located within a few meters along the fiber in real time by using developed software for this purpose.

A Rayleigh backscatter interrogator called Hyperbox has been developed and can reduce the number of agents needed with a strategic installation of such systems (in the order of dozens) with 24 hour, 7 days a week coverage at a cost-effective price tag. The US border with Mexico is large (3,145 km) and is even larger between the US and Canada (8,891 km).

Figure 1 Here is a block diagram for one Hyperbox interrogator to monitor 120 km of fiber. This system simultaneously monitors two 60 km fiber legs by splitting the pulse into two outputs as shown. (Image courtesy of Reference 1)

Disturbances can be easily detected due to the nature of Raleigh backscattering. It is sensitive to the 8th order of the index of refraction of the fiber as shown in the following equation describing Rayleigh backscattering:


(Image courtesy of Reference 1)

Components for such a system consist of using a very low noise fiber-coupled 1550 laser, an SOA (semiconductor optical amplifier) to pulse the laser through the optical circulator (first leg in Figure 1) which in turn sends out light to the buried fiber (second leg in Figure 1).

The received signal goes back into the circulator (second leg) and comes out of the third leg in Figure 1, gets amplified and coupled into the detector. The next stage filters the reflected signal, digitizes it and stores it for analysis.



Figure 2 The Hyperbox system (Image courtesy of Reference 1)


We can see a more detailed system diagram in the following block diagram:



Figure 3 A more detailed block diagram of Hyperbox (Image courtesy of Reference 1)


This is a possible first line of security.

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